For various reasons, such as a consequence of disease or injury, it is often necessary to implant a prosthetic knee joint into the leg of a patient. When doing so, it is obviously desirable to replicate the normal movement of an anatomical knee as accurately and precisely as possible. Various attempts have been made for this purpose.
Typically, whenever it has been necessary to implant a prosthetic knee joint, the accepted procedure has been to first remove a substantial amount of bone from both the distal end of the femur and from the proximal end of the tibia. A pad having a substantially flat surface is then anchored and cemented onto the proximal end of the tibia, with the flat surface exposed. A curved bearing surface is also anchored and cemented onto the distal end of the femur. During use, the curved bearing surface is then allowed to slide over the flat surface for articulation of the prosthetic joint. Unfortunately, when compared to the normal movement of an anatomical knee, with a prosthetic knee joint wherein a single curved surface articulates relative to a single substantially flat surface the resultant articulation is significantly limited. Further, although there may be some structure to limit articulation of such a prosthesis to only flexion and extension, stability problems can still develop whenever the surfaces do not effectively interlock. A prosthetic knee is particularly susceptible to this defect when one surface is substantially flat.
In addition to the purely mechanical problems which are encountered with prosthetic knee joints, there are also materials problems. More specifically, the materials which are often used in the manufacture of prosthetic knee joints have been found to sometimes be deficient in terms of biocompatability. For example, unless proper materials are used, it is possible for the body to reject the prosthesis or for the prosthesis to simply wear out. It is apparent that to overcome the wear out problem, materials which have extended longevity need to be used. Otherwise, the artificial joint must be replaced. It can also happen that the materials become ineffective for their intended purpose. For example, it is known that cement has a limited useful life for holding respective parts of the artificial joint on the femur and tibia.
Not unexpectedly, the process of securely attaching a prosthetic part to a bone can cause problems. A significant problem in this regard involves the amount of bone that must be removed in order for the body to accommodate the implanted prosthesis. Also, there is a phenomenon known as the "wave effect" which causes bone to assume a different resultant shape than originally intended. This "wave effect" results in a distorted and bulging surface, and predominantly occurs whenever an anchor pin or stake is driven into the bone.
In light of the above, it is an object of the present invention to provide a prosthetic knee joint which effectively replicates the normal anatomical movement of a knee. Another object of the present invention is to provide a prosthetic knee joint which conserves bone and uses viable tissue for reconstruction of the knee joint. Still another object of the present invention is to provide a prosthetic knee joint which provides extended longevity for the prosthesis by relying on boney ingrowth, rather than cement, for the connection of the prosthesis to the bone. Yet another object of the present invention is to provide a prosthesis which is effectively biocompatible and which reduces the autoimmune rejection phenomenon. Another object of the present invention is to provide a prosthetic knee joint which exhibits an effective stability. An object of the present invention is to also provide a prosthetic knee joint which is relatively simple to manufacture, acceptably easy to implant, and comparatively cost effective.